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CompTIA A+ Certification All-in-One Exam Guide

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EXAM TIP Remember the differences between the IMEI and IMSI

numbers for the CompTIA A+ 1001 exam. The IMEI number represents the

device. The IMSI number is tied to the user’s account with the carrier, and is

included with the SIM.

VPN

As you’ll recall from earlier chapters, VPNs establish secure connections

between a remote client and the corporate infrastructure, or between two

different sites, such as a branch office and the corporate office. VPNs are

typically implemented using tunneling methods through an unsecure network,

such as the Internet. In a client VPN setup, the host has client VPN software

specially configured to match the corporate VPN server or concentrator

configuration. This configuration includes encryption method and strength, as

well as authentication methods.

A site-to-site VPN scenario uses VPN devices on both ends of the

connection, configured to communicate only with each other, while the hosts

on both ends use their respective VPN concentrators as a gateway. This

arrangement is usually transparent to the users at both sites; hosts at the other

site appear as if they are directly connected to the user’s network.

VPNs can use a variety of technologies and protocols. The most popular

ways to create a VPN are to use either a combination of the Layer 2

Tunneling Protocol (L2TP) and IPsec (see Figure 24-22), or Secure Sockets

Layer (SSL)/Transport Layer Security (TLS). When using the L2TP/IPsec

method, UDP port 1701 is used and must be opened on packet-filtering

devices. In this form of VPN, users connect to the corporate network and can

use all of their typical applications, such as their e-mail client, and can map

shares and drives as they would if they were actually connected onsite to the

corporate infrastructure.

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